North Korea threatened Monday to launch an all-out offensive against South Korea and the United States over their annual military drills in the latest warning amid heightened tension on the Korean Peninsula.

"The army and people of the (North) will take military counteraction for preemptive attack so that they may deal merciless deadly blows at the enemies," the North's powerful National Defense Commission said in an English-language statement carried by the country's official Korean Central News Agency.

The commission also warned that major South Korean targets are within the North's firing range, and its nuclear strike capability can reach U.S. military bases in the Asia-Pacific region as well as the U.S. mainland.

"If we push the buttons to annihilate the enemies even right now, all bases of provocations will be reduced to seas in flames and ashes in a moment," the commission said.

The North's threat came as South Korea and the U.S. are set to launch their largest two-month joint exercise ever later in the day which will involve more than 300,000 South Korean and 15,000 U.S. troops.

The North claims the joint military drills are a rehearsal for a nuclear war against it. Seoul and Washington have said such exercises are purely defensive in nature.

The North's bellicose rhetoric is routine at the time of the Seoul-Washington drills, but the North has ratcheted up the tone of its threats amid the international community's move to slap it with sanctions over its nuclear and missile tests.

The United Nations Security Council on Wednesday unanimously adopted a fresh resolution to punish North Korea for its provocations.

It calls for mandatory inspections of all cargo going into and out of North Korea and a ban on exports of mineral resources, a major source of hard currency for the cash-strapped country.

North Korea conducted its fourth nuclear test on Jan. 6, followed by a long-range rocket launch last month, a move which outside experts view as a cover for a ballistic missile technology test.

North Korean leader Kim Jong-un ordered his military on Thursday to make nuclear weapons ready for preemptive attacks at any moment.

Kim made such remarks when he inspected the test-firing of what the North says was a new multiple rocket launch system. Seoul said the North fired off six short-range projectiles into the East Sea in an apparent expression of anger over the U.N. sanctions.

Experts said the North's military rhetoric appears to target its domestic audience to elicit allegiance in the face of the tougher sanctions and ahead of a major party event.

North Korea plans to hold the first congress of its ruling party in more than three decades in May, pushing its people into working hard in its "70-day campaign of loyalty." (Yonhap)